The reaction between aromatic diols and diglycidyl ethers is well established. In the articles entitled "Polyhydroxyethers. I. Effect of Structure on Properties of High Molecular Weight Polymers from Dihydric Phenols and Epichlorohydrin", the authors, Reinking, Barnabeo, and Hale, discuss the polyhydroxyether of bisphenol-A. (Journal of Applied Polymer Science, Vol. 7, pp. 2135-2144, 1963). The ether is formed by reacting bisphenol-A with epichlorohydrin to yield the polyhydroxyether of bisphenol-A with the following repeating unit: ##STR1## The article also discusses the use of connecting groups other than isopropenyl in the bisphenol and their effect on the glass transition temperature of the polyhydroxyethers. Such groups include ##STR2## to name a few.
The polyhydroxyether of bisphenol-A has a much higher molecular weight than commercial epoxy coatings resins, 45,000 versus a maximum of about 8,000. It also does not contain the terminal epoxide functionality so the polymer is thermally stable and can be fabricated by conventional thermoforming techniques. However, the present invention allows for polyhydroxyethers to achieve a molecular weight of greater than 100,000 and improved heat distortion temperatures. Specifically, the heat distortion temperature of the polyhydroxyether of bisphenol-A is 88.degree. C. at 264 psi. The present invention allows for heat distortion temperatures of greater than the boiling point of water. The present invention also eliminates the need for the crosslinking groups.
U.S. Pat. Nos. 2,698,315 and 4,072,656 disclose polyhydroxyethers prepared by reacting dihydroxybiphenol or tetramethyldihydroxybiphenol, respectively, with epichlorohydrin. Though these crosslinked products possess improved heat distortion temperatures relative to their bisphenol-A analogs, they have low molecular weights as compared to that of the present invention.
It has been discovered in accordance with this invention that when certain diglycidyl ethers are reacted with biphenols, high molecular weight polyhydroxyethers with higher heat distortion temperatures are formed. It is thus an object of this invention to provide such polyhydroxyethers for use in thermoforming processes such as extruded films, packaging, and coatings.